An integrated circuit, such as a dynamic random access memory (DRAM) includes passive devices, such as capacitors, and active devices, such as metal-oxide semiconductor field-effect transistors (MOSFETS), fabricated on a single substrate. In fabricating an integrated circuit to perform a particular function, the passive and active devices are coupled together. For example, a capacitor electrode is electrically coupled to a MOSFET drain or source to form a dynamic random access memory (DRAM) cell for storing information.
One method of coupling a capacitor electrode to a MOSFET drain or source includes the operation of directly coupling the capacitor electrode to the drain or source by fabricating the capacitor electrode at the drain or source. Unfortunately, several problems arise when a non-silicon electrode is directly coupled to a MOSFET drain or source. First, the electrode can experience oxidation, which interferes with the electrode conductivity and may cause unpredictable memory cell operation. Electrode oxidation is most likely to occur during capacitor formation processes performed in an O2 atmosphere. Second, atomic migration to and from a substrate, such as silicon substrate, may occur between the substrate in which the MOSFET source and drain are formed and other integrated circuit elements, such as the dielectric layer of a capacitor. Atomic migration alters the electrical properties of the integrated circuit elements and may cause unpredictable memory cell operation.
One solution to these problems is to form a contact structure having a barrier layer located between the electrode and the source or drain for blocking oxygen migration and atomic migration to and from the substrate. Unfortunately, a single barrier layer that effectively blocks both oxygen migration and atomic migration from the substrate may react with the conductive layer fabricated at the source or drain and cause unpredictable circuit operation.
For these and other reasons, there is a need for the present invention.